GN: fix mac build again

tools/flags/SkCommandLineFlags.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCommandLineFlags.h"
 #include "SkTDArray.h"
 #include "SkTSort.h"
@@ skipping 317 matching lines @@
                             flag->setDouble(atof(argv[i]));
                             break;
                         default:
                             SkDEBUGFAIL("Invalid flag type");
                     }
                     break;
                 }
                 flag = flag->next();
             }
             if (!flagMatched) {
-#if SK_BUILD_FOR_MAC
+#if defined(SK_BUILD_FOR_MAC)
                 if (SkStrStartsWith(argv[i], "NSDocumentRevisions")
                         || SkStrStartsWith(argv[i], "-NSDocumentRevisions")) {
                     i++;  // skip YES
                 } else
 #endif
                 if (FLAGS_undefok) {
                     SkDebugf("FYI: ignoring unknown flag '%s'.\n", argv[i]);
                 } else {
                     SkDebugf("Got unknown flag '%s'. Exiting.\n", argv[i]);
                     exit(-1);
@@ skipping 50 matching lines @@
 }
 
 }  // namespace
 
 bool SkCommandLineFlags::ShouldSkip(const SkTDArray<const char*>& strings, const char* name) {
     return ShouldSkipImpl(strings, name);
 }
 bool SkCommandLineFlags::ShouldSkip(const StringArray& strings, const char* name) {
     return ShouldSkipImpl(strings, name);
 }